Over the past decade tremendous progress has been made toward quantifying and understanding ozoneloss in the Arctic stratosphere. Today a variety of approaches exist to quantify the degree of chemicalloss over the course of an Arctic winter. Some have been used in a consistent way for many years andhave produced a record of the interannual variability. On the other hand a wide range of chemicalmodels have been used to understand the processes in the wintertime Arctic stratosphere and tocalculate the degree of ozone loss.<br><br>An active scientific discussion has started about the level of maturity of up to date chemical models ofthe polar stratospheric chemistry. How well are observations of the ozone loss rate reproduced? Howcomplete is our current quantitative understanding of the involved chemical and microphysicalprocesses? Are discrepancies between model results and observations larger than the combined knownuncertainties?<br><br>In the published literature the answers to these questions are controversial. Over the next few yearsone of the major challenges for the stratospheric research community will be to predict the future of theArctic ozone layer in a scenario of decreasing stratospheric halogen loading and possible changes inclimate. A solid assessment of our ability to reproduce currently observed ozone losses with modelcalculations is indispensable to determine the requirements for future research and to correctly interpretthe reliability of model based predictions.<br><br>To address these issues the Arctic Ozone Loss Workshop was held on 4-6 March in Potsdam,Germany, hosted by the Alfred-Wegener-Institute for Polar and Marine Research. The conveners (theauthors of this summary) were joined in a program committee by Georgios Amanatidis, Mike Kurylo, PaulNewman, and John Pyle. About 70 scientists from Europe, the US, Japan, Russia and New Zealandparticipated. The workshop was mainly based on poster presentations and discussion sessions. It waspart of DYCHO, a research project within the German AFO-2000 program and of QUOBI, an EC fundedresearch project, which are both part of the EU research cluster SOLO. The workshop was supported bySPARC.<br><br>